The Hawker Siddeley P.1154

It can justifiably be said that the Harrier is Britain's
greatest post-war aviation success. However, it had originally been
the RAF's intention to introduce a far more formidable 'jump-jet' to
the front line - the Hawker Siddeley P.1154. The cancellation of this
project in February 1965 was a huge blow to the prospects of the British
aircraft industry, with long-term consequences more damaging than the
cancellation of the TSR 2. The opportunity to provide the world's first
supersonic V/STOL fighter was lost, a capability that will now be provided
by the Joint Strike Fighter programme, in which Britain has only a minority
stake.

Artist's impression of an RAF P.1154

Competition and Commonality

The P.1154 originated in the rejection of subsonic V/STOL
aircraft, such as the Hawker P.1127, by both the RAF and NATO in the
early 1960's. In 1959 both institutions had drafted requirements, GOR345
and GOR-2 respectively, for a subsonic strike fighter based around the
P.1127. Further study resulted in both seeing such an aircraft as unattractive,
due to its limited payload-range and apparent vulnerability to supersonic
interceptors. With interest in an operational subsonic aircraft waning,
despite flight tests having only just begun, Hawker Aircraft at Kingston
began design work in early 1961 on a stretched, supersonic derivative
of the P.1127, under the direction of Ralph Hooper.

Designated P.1150, this used a Pegasus engine incorporating
plenum chamber burning (PCB) in the bypass air delivered to the front
nozzles. However, Hawker did not actively promote the P.1150 to potential
users in case it led to all remaining interest in the P.1127 evaporating.
Despite the loss of service interest in the latter, it needs to be borne
in mind that the practical experience gained from the P.1127 and Kestrel
continued to 'pour design knowledge' into the supersonic aircraft.

During August 1961 Hawker received specification AC/169
for a supersonic V/STOL strike fighter to meet NATO Basic Military Requirement
3. This called for a single-seat aircraft capable of flying strike missions,
with additional reconnaissance and interception capabilities. The key
mission was a lo-lo sortie of 250nm radius at Mach 0.92 with a 2,000
lb weapon load. The prospect of providing the NATO alliance with a common
fighter soon attracted most major aircraft companies in Western Europe
and America to enter the biggest international design competition ever
held. The Hawker entry was the P.1150/3, using a Bristol Siddeley BS.100/9
vectored thrust engine, the aircraft being re-designated P.1154 before
final submission to NATO in January 1962. The full results of the competition
became known in May, the P.1154 being declared technical winner, but
when financial and work-sharing considerations were added in the French
Mirage IIIV was judged to be of equal merit. As NATO had insufficient
funds for full development this was seen to rely on the member countries
moving ahead on their own initiative. Nevertheless, the P.1154 did receive
some financial support from NATO until December 1963, in the shape of
50% funding of PCB development for the Pegasus and BS.100.

In Britain, the RAF saw that the NBMR-3 competition
could lead to the kind of aircraft they needed to replace the Hawker
Hunter from 1968, in contrast to the subsonic GOR345/P.1127 aircraft
already studied. The Royal Navy also had a requirement for a Sea Vixen
replacement, to enter service after 1970. The Ministry of Aviation saw
an opportunity to develop the P.1154 for both Services and to break
the NBMR-3 impasse at the same time; Hawker received the draft of a
new joint requirement, OR356/AW406, in April 1962. It was soon clear
to the design staff that the two Services needed very different aircraft,
the RAF requiring essentially the NBMR-3 design while the Royal Navy
wanted a two-seat, high altitude interceptor to be catapult launched
from their carriers. Nevertheless, the prospect of saving £150 million
in development costs, which was earmarked to pay for a new aircraft
carrier, kept the Royal Navy from opposing the goal of commonality.
Similarly, the Hawker directors, including Sir Sydney Camm, wanted to
keep the aircraft common to both Services, as this would provide larger
orders for the company. This led them to play down the technical difficulties
that the firm's designers saw would occur in joint development.

As the design of the P.1154 was adapted to meet the
needs of the two Services the respective variants diverged from each
other to an ever-greater degree. The preliminary brochure submitted
in August 1962 saw the RAF and Royal Navy aircraft as being 80% common.
By the time of the more detailed brochure of May 1963 the situation
had reversed, with only 20% commonality between the two designs. This
growing divergence was mostly caused by the Royal Navy's demands. AW406's
insistence on two seats, large AI radar and two-shock inlets to achieve
Mach 2 at altitude led to considerable weight growth, necessitating
larger wings, while the catapult requirement led to a new undercarriage
layout. The waters were further muddied by a Rolls-Royce proposal to
substitute twin Spey engines, modified to use vectored thrust and PCB,
in place of the BS.100. Despite all this, the design for the RAF remained
fairly constant, being essentially the same as that proposed for NBMR-3.
While the naval aircraft remained fluid, Hawker began detail design
and mock-up construction of the RAF variant.

Detail of the P.1154 mock-up at Kingston,May 1964, showing the
engine nozzles in the vertical position.

Lower aft view of the mock-up, with the engine nozzles horizontal.
.

By June 1963 it was clear that the divergence between
the two versions meant that, in effect, two separate aircraft were being
proposed, with the airframes, avionics and systems differing between
them. The Defence Research Policy Committee therefore ordered that a
wholly common, Bi-Service version of the P.1154 be designed. A brochure
for this was hastily submitted in August 1963 and it quickly became
obvious that it was unacceptable to both Services. The Royal Navy had
to give up the second crewmember and two-shock inlets, while the provision
of wing folding and catapult facilities increased weight, to the detriment
of range and weapon load, in RAF missions. The P.1154 had reached crisis
point, with complete cancellation on the cards. Numerous alternative
aircraft purchases were investigated from November 1963 to January 1964,
including a developed P.1127 for the RAF or dissimilar P.1154 variants
tailored to the needs of each Service. The eventual decision, announced
in February 1964, was to adapt the McDonnell F-4 Phantom with Spey engines
for the Royal Navy and to develop a version of the P.1154 specifically
for the RAF, this being seen as the most cost effective solution to
the two Service's requirements.

New Beginning

The re-focussing of the P.1154 as a single seat strike
fighter for the RAF allowed Hawker Siddeley to concentrate their efforts
on a firm objective after the trials of the previous two years. It meant
large reductions in development costs, and clearer planning for the
manufacture and flight-testing of the development batch aircraft, could
be envisaged. Both the RAF and Hawker Siddeley's technical staff were
relieved by the elimination of the commonality requirement, and the
P.1154 now began to make real progress, moving from design to development.

By early 1964 the industrial base of the project had
been strengthened by the formation of Hawker Siddeley Aviation as a
consolidated company. The P.1154 was to be developed by the Hawker Blackburn
Division, with John Fozard as Chief Designer and Barry Laight (former
leader of the Buccaneer team) as Chief Engineer. This division had been
specifically formed in 1963 to allow the aircraft to benefit from the
experience of the 'weapons system' approach that had been used in the
Buccaneer programme, the P.1154 being expected to follow a similar development
path. While Hawker Siddeley questioned the degree of control that the
Ministry of Aviation had over areas such as the avionics, believing
they could perform these functions much better themselves, they agreed
to appoint a Programme Controller to oversee the project and to adopt
the PERT management system. Both measures were recent innovations, aimed
at avoiding the financial errors and timescale overuns that had afflicted
the TSR 2 programme.

While the industrial organisation was taking shape,
the RAF was refining its requirements. The key features they wanted
from the P.1154 were V/STOL and supersonic speed. Outside of these they
were willing to simplify the aircraft considerably, to save time and
money. While being designed to fulfill essentially the same mission
as that of the NBMR-3 submission, much use was made of the work undertaken
during the commonality debacle. The airframe was basically that of the
Bi-Service design, with all the naval features removed. Once the project
received the green light in February 1964 it was constantly reviewed
in order to keep the design as simple as possible. The previously projected
use of digital computing was dropped, in favour of an analogue nav-attack
system that would be 20% cheaper to produce. Manual, rather than automatic,
terrain following was adopted while the requirement for the aircraft
to carry AS.30, Bullpup and T.V. guided AJ.168 (Martel) missiles was
dropped later in the year. The need for the P.1154 to be fully nuclear
capable was also relaxed in order to further simplify the aircraft.
By April 1964 the RAF had issued a revised OR356 and Hawker Siddeley
had begun manufacture of assembly jigs and detail parts for the development
batch aircraft at its Kingston and Hamble factories.

Wing assemblies at Hamble, February 1965.

The first P.1154 fuselage in the jig at Kingston, February 1965.

August saw Hawker Siddeley submit their detailed design
to the Ministry of Aviation, as called for under holding contract KC/3B/5.
This outlined a development programme involving eight aircraft, with
first flight two years from the instruction to proceed (ITP) and initial
CA release five years from ITP. It was agreed in October 1964 that,
in the light of the work already done, the ITP could be regarded as
having been reached in July 1964. Rolls-Royce were allocated £9 million
of development work on the BS.100, including conversion of the Vulcan
B.1A test-bed, XA896. Two Hunters were to be converted to test the nav-attack
system, designated HS.1172. Hawker Siddeley and the Ministry of Aviation
continued to discuss detail points that affected the programme, the
most important being the continuing lack of orders for the radar and
inertial nav-attack system. Both these items had been awarded to Ferranti,
but contract signature was suspended until the company could pay back
excess profits gained on the Bloodhound missile programme. This hold-up
was causing serious worry to Bob Lickley, Chief Executive of the Hawker
Blackburn Division, as he thought it could delay the full release of
the P.1154 weapons system by up to 18 months from the planned service
entry date of July 1969.

Nevertheless, the RAF continued to refine its scheme
for the deployment of the P.1154, the name Harrier having been provisionally
chosen for the aircraft. Plans went ahead for eight operational squadrons,
two each in the UK, Germany, Middle East and Far East. The aircraft
would operate from both main and forward bases, such as short airstrips
or stretches of road, with four or six aircraft operating from the latter.
Unsupported forward sites could also be used, reducing mission capability.
Although it would have been capable of true vertical take-off, the normal
means of operation would have been to use a short take-off, in order
to minimize ground erosion and hot gas re-ingestion problems, and to
maximise payload. Rolling vertical landing, with the engine throttled
back, was to be employed at the end of each mission, with vectoring
of the engine nozzles in forward flight envisaged to increase maneuverability,
at the cost of significant deceleration. All of these techniques were
to be explored 'in the field' during the Tripartite trials of the Kestrel
in 1964-65. In the ferry mission extended wing tips were added to the
aircraft, the 'combat tips' being stored in the rear fuselage. RAF P.1154s
were to be capable of operating from all Royal Navy carriers, the aircraft
having a folding nose to help it fit their deck lifts.

Definitive Design

All the design and operational characteristics worked
out during 1964 were embodied in specification SR250D, issued in October.
The P.1154 submitted to this specification had a length of 57ft 6in,
span of 28ft 4in and height of 12ft 6 in. The low aspect ratio, 269
sq. ft wing used a 'peaky' aerofoil, with a leading edge sweep of 41.2
degrees. The airframe was stressed to 7.5g for combat and 3g for ferry
missions. The aluminium and titanium structure was designed for a 3,000hr
fatigue life; extensive use of chemical etching, integral machining
and bonded honeycomb helped to keep down weight. To cope with bird-strikes
at low level the windscreen and leading edges were designed to withstand
a 1lb bird impacting at 600 kts. The bicycle undercarriage, stressed
for descent rates of 10 ft/sec, employed low-pressure tyres, with the
outriggers taking a significant proportion of the aircraft's weight
in order to increase stability during ground maneuvering.

The heart of the P.1154 was its Bristol Siddeley BS100/8
Phase II vectored-thrust engine, at the time the most powerful jet engine
in the Western world. This was installed around the aircraft's centre
of gravity and could be removed via a detachable 'tray' underneath the
fuselage. An electronic control system was provided for the engine's
main functions. The four engine nozzles had 16 degrees anhedral to improve
propulsive efficiency, with the PCB equipped front pair discharging
past variable area ramps. Peak temperature of the front jets was 1,400K,
the rear jets having a maximum of 1,000K.

On the test-bed this engine had a 'short'
rating of 35,900 lb thrust for 20 seconds using PCB, maximum 'normal'
thrust being 33,900 lb. Water methanol injection was to be used
to restore thrust in hot and high conditions. With PCB off maximum
thrust was 26,200 lb. Mass flow was 490 lb/sec, by-pass ratio 0.9
and overall pressure ratio 11.45. The minimum specific fuel consumption
of 0.6 lb/hr/lb was achieved at 14,400 lb thrust, SFC at maximum
thrust being twice this figure. In order to reduce technical and
financial risk, compared to the earlier 'all new' BS.100/9 proposal,
the BS.100/8 used the high-pressure compressor of the Olympus B.Ol.22.
The annular combustor and lightly loaded four-stage titanium fan
were both based on Pegasus 5 experience, suitably scaled. For engine
starting and prolonged ground loiter at dispersed sites a gas turbine
starter/APU was fitted. The air intakes had variable geometry lips
to provide optimum pressure recovery in all flight regimes, with
blow-in doors operating at low speeds. A large ventral airbrake,
mounted well forward, acted as a dam to alleviate hot-gas re-ingestion
problems. Internal fuel capacity was 1,300 Imperial gallons.

One of the six BS.100 engines built - the garish colour scheme
was due to the use of heat sensitive paint for tests.

Empty weight of the P.1154 was projected as 20,100 lb,
maximum loaded weight being 40,050 lb in the ferry condition. Each wing
had two pylons, rated at 2,000 lb inboard and 1,000 lb outboard, while
the fuselage could take either a single centreline pylon rated at 2,000
lb or dual pylons of 1,000 lb each, maximum weapon load being 8,000
lb. For combat missions two 300 Imperial gallon tanks could be carried
on the inboard wing pylons, replaced in the ferry role by 400-gallon
tanks, a 200-gallon tank under the fuselage and a detachable flight
refueling probe on the starboard air intake. The duplicated, fully powered
flying control system was backed up in jet-borne flight by reaction
controls in the wingtips and tailcone, using high-pressure air bled
from the engine. Both autostabilisation and a simple autopilot were
fitted. In case of engine failure, a ram air turbine could be extended
from the rear fuselage to sustain electrical and hydraulic power. For
emergency landings a 1.5g arrester hook was fitted under the tail.

Partial cutaway of the aircraft - note the airbrake
mounted forward and the variable intake lips.

Capabilities and Costs

For strike missions the P.1154 would have carried low-drag
and retarded 1,000 lb bombs, cluster bombs and napalm tanks. Stand off
attack could be carried out using SNEB rockets and the anti-radar AJ.168
missile. In the air-to-air role up to four Red Top missiles could be
carried on the wing pylons, with underfuselage 2in rockets or twin 30mm
Aden guns as secondary armament in either role. In the reconnaissance
mission a pod carrying optical linescan, sideways looking radar and
a pair of oblique cameras was schemed, although this was thought to
pose some problems and simpler equipment was looked into. The aircraft
was to be permanently fitted with an F.95 camera in the nose, in addition
to its monopulse radar. The latter was able to provide terrain avoidance
information on the pilot's head-up display and ranging on surface and
airborne targets. Allied with the inertial navigation system, air-data
computer and moving map it would provide an accurate system for low-level,
single pass attacks. The high speeds envisaged at low altitude led to
the adoption of a single piece windscreen to increase the pilot's forward
field of view; a Martin-Baker zero-zero ejection seat allowed for his
escape at all airspeeds.

Radius of action was affected by both climate and the
warload of the aircraft. In typical missions (I.S.A. + 15C at sea-level,
2,000 lb load) and utilising a rolling vertical take-off (500 ft to
50 ft, ground run 50 ft) a lo-lo radius of action of 210 nm was envisaged.
With a short take-off (1100 ft to 50 ft, ground run 220 ft) and full
internal fuel a lo-lo radius of 280 nm was possible, cruising at Mach
0.92. With combat tanks a radius of 405 nm was forecast in the same
regime. If water injection was used in temperate climates it was hoped
that an extra 25 nm could be added to the potential radius. A hi-lo
profile could potentially double range, while in the air-to-air mission
a loiter of 160 minutes, 100 nm from base was possible with maximum
combat fuel and two Red Top missiles. Maximum speed at altitude with
PCB on was Mach 1.7, falling to Mach 1.13 at sea level. Even in cold
thrust the aircraft could achieve Mach 1.1 with two Red Tops, allowing
it to 'supercruise' during interception missions.

While the first BS.100 engine went on test at Patchway
in October 1964, the RAF had drawn up an additional requirement, ASR382,
for an operational two-seat trainer version of the P.1154. The design
that Hawker Siddeley submitted was modified to have a front fuselage
with stepped tandem seating and a rear fuselage plug, bringing overall
length to 61ft 1in. By relocating avionics from the nose to the rear
equipment bay, and by reducing internal fuel to 1,174 gallons, the trainer's
centre of gravity could be maintained. The RAF planned to buy 25 of
these in addition to 157 single-seat aircraft, with training supported
by simulators. Overall development costs were officially estimated (taking
into account TSR.2 experience) at £170-200 million, with an additional
£10 million for the two-seater. Unit costs were put at £1 million for
the single-seat aircraft and £1.2 million for the trainer. Final approval
was given for development, based on these figures, by the Weapons Development
Committee in November 1964. Bristol Siddeley were planning to develop
the BS.100 to 39,250 lb thrust by 1972, restoring any performance shortfalls
caused by weight growth during development. This was estimated by the
Ministry of Aviation to be potentially as high as 8.5%, although Hawker
Siddeley hoped to limit weight growth to 4% over the August 1964 brochure
figure.

Front fuselage for the 'final installation model' P.1154.

Two-seat trainer P.1154 front fuselage mock-up.

Cancellation

In the same month that the BS.100 began bench tests,
a Labour government came to office dedicated to making economies in
defence expenditure. They initially focussed on equipment programmes,
the high costs of combat aircraft drawing special scrutiny. Almost to
a man the RAF was dedicated to preserving the TSR 2, as it was seen
to provide the core capability that justified the Service's full independence.
In the ongoing debate over the East of Suez commitment, in which they
were striving to oust the Royal Navy's carrier task groups from their
key role, the RAF saw the TSR 2 as their main weapon. With the further
integration of the Service ministries under a centralised Ministry of
Defence, the idea that the army might take over the tactical air support
mission, and with it the future P.1154 squadrons, seemed a further possibility.
The RAF decided not to oppose the cancellation of the P.1154 too vigorously
and to gamble all on the TSR 2.

The reason given in the House of Commons for cancelling
the P.1154, on 2nd February 1965, was that it would not be in service
in time to replace the Hunter in 1969. Although this was probably true,
the records show that the RAF had accepted the anticipated delay in
introducing the P.1154 until 1970-71, with the Hunter being considered
adequate until 1972 in any case. The 1969 date had continued to be publicly
quoted merely as a way to keep Hawker Siddeley applied to the task after
the commonality fiasco. The P.1154 was replaced in the RAF's plans by
a combination of Spey engined Phantoms and a promise to develop, although
not necessarily to procure, an operational P.1127/Kestrel derivative
using much of the nav-attack system, and some detail design, from the
P.1154. However, this subsonic V/STOL development was seen as very much
a political consolation prize by the RAF and Hawker Siddeley. Both organisations
were fully aware that the P.1127 had been rejected for operational purposes
four years previously and, while it had matured a great deal since then,
might only be developed in the short term to sweeten the bitter pill
of the P.1154's cancellation.

By early 1965 over 5,000 men were directly employed
on the P.1154, with more than 750,000 engineering hours expended and
£25 million committed. With the development aircraft in assembly, and
the forecast operational difficulties largely side-stepped, the cancellation
of the P.1154 was a huge waste of potential. Although the TSR 2 was
a triumph of 1950's technology, its prospects of being exported looked
extremely poor due to its high costs and complexity. On the other hand,
the P.1154 represented the last all-British entry in the key supersonic
fighter market that has provided the bulk of exports for combat aircraft
in the 1970's, 80's and 90's. At the time of its cancellation many countries
were still pursuing the goal of survivable, effective airpower that
aircraft such as the P.1154 offered. While the subsonic Harrier has
proved modestly successful in the export field, the availability of
the more capable P.1154 could have strengthened the customer base for
V/STOL combat aircraft, providing a much greater success in the one
area of aviation where Britain had genuinely led the world.